Concerned about the dangers of consistently climbing obesity rates, Los Angeles County officials launched a new public health campaign Thursday to help residents control their portion sizes.

Choose Less, Weigh Less - aims to raise awareness about recommended calorie limits and to get residents to consume fewer calories.

"It is no secret that portion size, as well as our waistlines, have expanded over the last two decades," Jonathan Fielding, director of the county Department of Public Health, said during a press conference in downtown Los Angeles. "Unfortunately, we have become accustomed to these oversized portions."

And that is causing residents to eat far more than the recommended 2,000 calories a day, leading to higher rates of obesity, he said.

Nearly 24% of county residents were obese in 2011, according to new data released Thursday. The rates show a 74% increase since 1997, when 13.6% of residents were obese. There continue to be disparities among populations, with obesity rates higher among Latinos and African Americans than whites and Asians. Obesity is also more prevalent among people with less education and lower incomes.

Fielding said the primary reasons for the increase are the fact that residents are eating more food and becoming more sedentary. The campaign will educate residents about how they can take small steps to make significant changes in their health, he said.

The obesity epidemic is also expensive, with lost productivity and healthcare expenditures costing the county $6 billion annually, said County Supervisor Zev Yaroslavsky. Obesity is linked to diabetes, heart disease and other illnesses.

Yaroslavsky said the costs will continue to rise unless the county takes more aggressive actions. While county leaders will continue promoting healthier eating, they said Thursday that residents should start controlling how much they eat.

The campaign will include advertisements on buses, billboards, television, radio and social media. The colorful ads show photographs of different sizes of meals and the number of calories saved by eating the smaller size.

The county also plans to work with restaurants to get them to offer smaller portions. In addition, public health officials are researching other options such as taxes on sugar-sweetened beverages or bans on certain larger-sized drinks.